As light-sensitive materials to which the present invention can be applied, there are, for example, light transmissible electrophotographic films, silver salt films (silver dry films comprising silver halide or an organic silver salt such as silver behenate, silver benzotriazole, etc., as a main component, as described in Japanese Patent Publications Nos. 2096/63, 4921/68 and 4924/68, etc.) and heat developable films as described in Japanese Patent Publications Nos. 35484/79 and 2687/78.
For the above described light-sensitive materials, the prior art will be illustrated with reference to only the case of light transmissible electrophotographic materials, but the discussion thereon applies to the other light-sensitive materials with equal force.
A process which comprises forming a toner image on an electrophotographic light-sensitive material and thereafter transferring the toner image to plain paper and a process which comprises forming an image on a recording material comprising an electrophotographic light-sensitive material on a base such as paper or film, etc., are known as processes for forming images by electrophotography.
In the early days of the electrophotographic art, raw materials used for electrophotographic light-sensitive materials were commonly inorganic substances such as selenium, cadmium sulfide, zinc oxide, etc. In recent years, however, organic electrophotographic light-sensitive materials, for example, electrophotographic light-sensitive materials composed of poly-N-vinylcarbazole and 2,4,7-trinitrofluorene-9-one (U.S. Pat. No. 3,484,237), those in which poly-N-vinylcarbazole is sensitized with pyrylium salt dyes (Japanese Patent Publication No. 25658/73), electrophotographic light-sensitive materials comprising an organic pigment as a main component (Japanese Patent Application (OPI) No. 37543/72 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application")) and electrophotographic light-sensitive materials comprising an eutectic crystal complex composed of a dye and a resin as a main component (Japanese Patent Application (OPI) No. 10735/72), etc., have been proposed; they are easily processed by applying the organic photoconductive substance directly or by mixing it with a suitable binder.
Further, it has become possible to produce light transmissible electrophotographic recording materials by selecting a suitable organic photoconductive substance and a base. Disclosure thereon occurs in Optical Eng., Vol. 20, No. 3, page 365 (1981).
Generally, recording materials for electrophotography have excellent characteristics as compared with silver halide photographic recording materials conventionally used.
For example, electrophotographic recording materials are easily produced and processed, packing is simple and processing such as development, etc., can be simply carried out as they are not light-sensitive until they have been subjected to charging.
Further, as a singular characteristic of the electrophotographic process, there is the fact that exposure and development can be repeatedly carried out using one recording material. Namely, in silver halide recording materials if a developed image is once formed, another image cannot be recorded on the same recording material. However, electrophotographic materials have the characteristic that the image can be recorded at a desired position of the recording material whenever recording is required.
Conversely, in the case of long film of electrophotographic recording materials, there is the fault that when charging, exposure and development are electrophotographically carried out, the electrically conductive substance present comes off during conveying and adheres to the nonexposed surface or the electrostatically charged surface of the exposed light-sensitive layer to cause a part of electric charges present to "leak off", whereby the image is electrostatically damaged to cause image defect.
With respect to the above problem, it is disclosed in Japanese Patent Publication No. 6150/71 that charge removal zones can be provided on both sides of the long film in the lengthwise direction to help to overcome the same.
Another fault of electrophotographic processes is that the image is inferior in resistance to friction and is easily damaged when repeatedly used; this is because toner adheres only to the uppermost layer of the recording material to form the desired image.
With respect to this problem, charge removal zones as described in the above described Japanese Patent Publication No. 6150/71 show some effect as image protective zones, but they are not satisfactory because the charge removal zones wear during repeated use.